Machine elements which absorb energy applied by periodic compressional stress



May 11, 1954 R. s. DEAN 2,678,292

MACHINE ELEMENTS WHICH ABSORB ENERGY APPLIED BY PERIODIC COMPRESSIONAL STRESS Filed Jan. 25, 1952 u 600 u I Q 2 5e ELEA 5 400 1 O \o E m 200 0 Z I o I F I00 w 2 LL] .J

5000 IOOOO |5ooo LOAD POUNDS mn LOAD RELEASE M I 5|O// I MPREQ/ 2 Abe/O EA! d E v a y 9 z 5000 10000 3 COMPRESSION m POUNDS 3 5O ABOVE BASE. LOAD I U I 200/ 5 z j l N VE NTOR flima d 5 Um Patented May 11, 1954 MACHINE ELEMENTS WHICH ABSORB EN- ERGY APPLIED BY PERIODIC COMPRES- SIONAL STRESS Reginald S. Dean, Hyattsville, Md., assignor to *Chicago Development Corporation, Riverdale, Md., a corporation of Delaware Application January 25, 1952, Serial No. 268,357

1 Claim. 1

This invention relates to machine elements for absorbing vibrations. It has for its aim the provision of machine elements which absorb energy applied by periodic compressional stress, and transform this energy into heat while undergoing a minimum of over-all length change. This application is a continuation in part of my application, Serial 108,763 filed August 5, 1949 now abandoned. My invention consists of an element formed by the combination into a composite sheet or strip consisting of a manganese-copper alloy having a Poissons ratio of from 0.5-0.7 and another metal or alloy having a Poissons ratio of 0.25-0.40. For the functioning of such an element in a practical manner, it is necessary that both of the laminae have an elastic limit of at least 10,000 p. s. i. In addition the material selected for laminae must be capable of fabrication, in the usual manner, that is, by rolling. It is preferable that the two laminae have approximately the same coefiicient of expansion. For the lamina having a Poissons ratio of 0.25-0.40, many common metals and alloys are available, such as brass, bronze, mild steel and nickel alloys. For the lamina with the high Poissons ratio, I have found only one series of alloys to be useful, namely copper-manganese alloys containing 79-85% manganese, and quenched from a temperature of 800-900 C. I do not claim these alloys as my present invention, but only a machine element made by bonding them in a condition having a Poissons ratio of 0.5-0.7, to another metal having a Poissons ratio of 0.25-0.40.

Example I In order to most effectively use the high Poissons ratio of the manganese alloys, I make a twolayer bonded bi-metal, the layer other than the manganese alloy being a material with normal Poisson ratio, such as steel. I have found that the highest Poissons ratio is obtained by using an 30% Mn, 20% Cu alloy quenched from the gamma field, that is 850-900 C. The Poisson ratio for such material is 0.7. I take, for example, a number of discs of such bimetal and quench from 850 C. This introduces a certain amount of warping so that I now grind the discs perfectly flat on both sides. The discs are then stacked, each one being reversed with respect to the one below it. When pressure is applied to such a stack of discs, the manganese alloy expands laterally more than the steel andthe disc becomes convex in the direction of the manganese alloy. Since the discs are alternately reversed, this causes a tendency to increase the length of the column which must be overcome by more pressure. The result is that considerable pressure range exists where increased pressure does not result in a proportionate decrease in height. Since this phenomenon is reversible within the elastic range, the energy of a vibratory force may be absorbed and released as heat by a column of such discs with almost infinitesimal overall amplitude of vibration of the column.

A specific example of this embodiment of my invention is illustrated in Figure I and Figure II. These figures show graphically the results of applying and releasing pressure on a stack of 34 one inch square bonded laminated .0375 inch thick, -20 manganese copper alloy and .0375 inch thick low carbon steel, each laminate being reversed with respect to the one next to it.

When an initial load is applied after a preliminary seating operation, there is at first a fairly rapid decrease in length due to compression of the material and then a slower decrease due to the expansive action of the curvature due to the different Poisson ratio of the laminae. When the load is released, the high internal friction of the manganese alloy laminae retard the loss of curvature of the plates and there is almost no increase in length until the applied pressure falls to a fraction of the applied load. The length then increases rapidly but at the ordinary rate of pressure release does not recover the original length before the load reaches zero. This is shown in Figure I for the specific example described.

If it were possible to apply a tensile load of the same magnitude and remove it, the stack would then be lengthened by the same amount that it was shortened by the compressive load. Since it is not possible to apply a tensile load to such a stack, a similar effect is produced by loading and reloading around an initial pressure of 5,000 pounds. Specificially, the stack is loaded to 5,000 pounds and then a load-length curve taken from this base line. The load is then removed to 5,000 pounds and the length load curve taken to this point. All load is then removed, corresponding to the application of a tensile stress, and the base load of 5,000 pounds again applied and a load-length curve taken as before. The result of this procedure is shown in Figure II and illustrated the energy loss in such a system when used, for example, as a shock absorber. The similarity to elastic hysteresis will be evident. The magnitude of the energy loss in each cycle, however, is of a higher order.

and a Poisson's ratio of 0.250.4,70, said tbimetall 10 being so disposed that the ivibratoryistressris;applied compressively to thepia'te.

References Cited in the file of this patent Number 5 2,259,459 2,349,577

Number UNITED STATES PATENTS Name Date Dean Oct. 21, 1941 Dean May 23, 1944 if FOREIGN PATENTS Country Date Great Britain June 18, 1941 my l1... 1.1- 

